Optimism among American homebuilders was unchanged in January, snapping a six-month slide, as borrowing costs fell and consumer confidence improved.

The National Association of Home Builders/Wells Fargo’s index of builder sentiment held at 57. The median forecast in a Bloomberg News survey of 16 economists called for a gain to 58.

“Some softening of long-term interest rates since early December helped buoy builder attitudes,” the chief economist of the Washington-based group, David Seiders, said today. “Consumer confidence has rebounded nicely from post-Katrina lows.”

Mortgage rates are likely to resume their climb, the home builders’ group has said, cooling a five-year housing boom that has helped fuel economic growth. Companies including Toll Brothers Incorporated predict sales will rise more slowly this year.

Forecasts in the Bloomberg News survey ranged from 54 to 62. Readings greater than 50 mean builders consider the outlook for sales to be positive.

The homebuilders’ gauge of buyer traffic was unchanged at 40. The current sales measure slipped to 62 from 64, and expectations for the next six months held at 65. Confidence fell in the Northeast, South, and West, and rose only in the Midwest.

The housing market has been the main driver of the American economy this decade, accounting for 50 percent of the overall growth and more than half of the private payroll jobs created since 2001, Merrill Lynch said in a report on August 15.

Home sales set records each year from 2001 to 2004, and a government report on sales in December, to be released on January 27, will probably show another record for 2005, according to economists.

“When we look back a year from now I think we’ll recognize the summer of 2005 as the peak of the housing boom,” the chief economist at National City Corporation in Cleveland, Richard DeKaser, said before the report.

In November, new home sales fell by the most in 11 years, and a record number of unsold homes was left on the market. Sales of previously owned homes fell to an eight-month low, and the number of unsold homes was the highest since 1986.

Mr. DeKaser said he expects homeprice appreciation to slow to 4% from 8%. The median price of a new home rose last month to $225,200 from $224,500 a year earlier, according to a December 23 report from the Commerce Department.

Fixed 30-year mortgage rates have moderated as signs of tamer inflation spurred purchases of 10-year-Treasury notes, pushing yields down. Mortgage rates are tied to the yield.The rate on a 30-year mortgage fell to 6.15% last week from a two-year peak of 6.32% on November 17. The rate has averaged 9.5% since 1980, according to Freddie Mac, the second-biggest source of money for American home loans.